His Cambiemos (Let's Change) movement won in 13 of Argentina's 23 provinces, including the five biggest population areas, official results showed. Despite the gains, he fell short of an overall majority in congress.

"We realised that many things can change, we realised that we could, we were encouraged by change, we overcame fear and resignation and reality accompanied us and is accompanying us," said Mr Macri, who is expected to run for re-election in 2019.

More than 33 million Argentines were eligible to take part in the vote, which saw a third of seats in the Senate contested, along with half of those in the lower house of congress.

Ms Fernández, who governed the country from 2007 to 2015, came in a distant second in the race in the province of Buenos Aires, the country's most populous.

Despite not coming first, she secured enough votes to make it into the Senate.

She thanked voters saying her party Citizen's Unity would remain a firm opposition to Mr Macri's economic agenda.

The ex-president, who faces corruption charges, still enjoys support among millions of low-income Argentines who benefited from her generous social spending. But critics say her populist policies damaged the economy.

She denies any wrongdoing saying the accusations are politically motivated.